1. FIELD OF THE INVENTION
This invention relates in general to devices for adding moisture to gases which are delivered to a patient for breathing and in particular to a new and useful device for wetting respiratory gases.
2. DESCRIPTION OF THE PRIOR ART
When exhaling a patient loses water in each exhaling phase due to the wetting of the air in its passage through the lungs. Care must therefore be taken when respirating a patient that water is supplied to the respiratory gas in each respiration phase in order to compensate for the water lost.
An atomizer is known for supplying liquid particles into a main gas current conducted to the patient and in such a construction an atomizer nozzle is surrounded by a jacket. In order to shield the liquid particles from the main gas current, its bottom end protrudes into the main gas current below a point at which the liquid impinges on the impact surface to divide the liquid particles. The liquid particles are distributed with the atomizer air current inside the jacket. The larger liquid particles which are undesired for therapy then drift down while the small liquid particles enter the main gas current and are fed to the patient. This arrangement is elaborate in its design and is used for supplying atomized medicine for long term therapy. A disadvantage of the known device is that the respiratory air cannot be heated. As far as wetting takes place it is not controllable. The sterilization of the apparatus also presents difficulties.
A known apparatus for wetting and heating air which is to be inhaled by an artificially respirated patient, consists of a tank for the water to be coverted to steam at a desired temperature. The tank is heated from the outside. It can be removed from the heating system for sterilization. The tank has a cover which provides an air space above the water level. Conducting means transfer the heat to the evaporation surfaces in the air space above the water level. The steam in the air space is absorbed by the respiratory air flowing through the air space and it is fed to the patient. Heat control means control the temperature and the moisture content. Another heater in a part of the wetting apparatus forming a tube is so designed that the temperature rise in the respiratory air in this part of the arrangement is equal to or greater than the temperature drop of the air thus heated on its way between the outlet of this heater and the patient. The maximum desired temperature is not exceeded. The object of this additional heater which complicates the arrangement is to avoid the formation of condensate. The engineering effort of the entire system is quite considerable. The total amount of water must be heated. Special regulating and control means are required. Furthermore, it is disadvantageous that the sensitive electrical parts of the apparatus must be disconnected before it can be stabilized with any degree of reliability. The great air space in the tank makes it difficult to maintain a constant volume of the respiratory air to be conducted therethrough.
Another known gas wetting apparatus for a respirator contains a water evaporation chamber for evaporating water at a water level. The water to be evaporated is supplied through a water filling connection with a float seal. The float seal can also be provided in a separate float chamber. The two chambers the evaporation chamber and the float chamber, are then connected with each other through a water conduit. The pressure between the gas compartments of the two chambers is equalized by a gas connection in the form of an opening or pipe having a small cross section. In order to insure the evaporation of the water on the surface in the evaporation chamber, a heating element is arranged in the water of the evaporation chamber. The flow chamber has an overflow duct closed by a float actuated valve so as to prevent a rise in the water level when the float seal on the water filling connection does not work properly due for example to a calcuim deposit, fouling, etc. In this complicated gas wetting apparatus the gas to be wetted is enriched with water above a water surface. In order to obtain a sufficient amount of steam, the evaporation surface and hence the entire water evaporation chamber must be large. The evaporation also depends to a great extent on the temperature of the water and on the velocity of the streaming gas as well as the resulting cooling of the water surface. An exact control is therefore very complicated unless exact dosing is not necessary. The sterilization of the evaporation chamber must either be effected together with the flow chamber and the float seal in the overflow valve or the gas wetting apparatus must first be disassembled.
Another known apparatus for wetting the respiratory air with a collecting vessel for the condensate contains an evaporated insert in the housing that is traversed both by the respiratory air and the exhaling air. This evaporator insert has a heating element. It is traversed by a water conduit into which the water to be evaporated is introduced. Below the housing is connected a collecting vessel into which the evaporated water or the condensate is introduced either through a nozzle or through a float valve. The mixing of the steam issuing from the water conduit with the respiratory air is effected in the clearance space of the housing where the respiratory air is introduced. The air leaves again to flow in the air feeding system to the patient after it has been heated by the heating element and has mixed with the steam issuing from the water conduit.
The regulation of the water supply to the evaporated must be very sensitive because only steam is to escape from the water conduit. But if the heating temperature is too high, deflagrations will occur so that the water and the steam are ejected. The clearance space of the housing is relatively large due to the respiratory air which flows through the housing. Outside of the evaporator insert over which both the respiratory air and the exhaling air must pass, the temperature is low in the clearance space, as is proper for heating the respiratory air, but this also tends to enhance the growth of bacteria. The necessary disinfection of the device is not simple and can only be done after completely disassembling the apparatus.